I worked on this same problem for a previous employer, a major hard drive
vendor. As you correctly stated, there are huge combinations of
variables. What you need to model is the entire transmission plant and not
just one component (the backplane) in it. The other critical components are:
1) the multi-mode terminators at each end,
2) the multi-mode host adapter transceiver IO cell and the hard drive SCSI
ASIC cell,
3) combination of different twisted pair and round SCSI cables allowed by
the SPI-3 standard,
4) bulkhead VHDC and internal SCA-2 connectors,
5) up to six inches of differential pcb traces on the host drives
including vias,
6) up to three inches of pcb trace stub on each of the 15 drives,

The list goes on, this is a complex problem that is even more complicated
by lack of reliable IO cell models and downward compatibility issues
inherent in SCSI. Remember to repeat your simulations for single-ended
Fast SCSI, Ultra 2 LVDS, Ultra 160 MByte/s, and perhaps Ultra 320.

Good luck,

-Farrokh Mottahedin

At 01:00 AM 1/10/01, =?big5?B?Sm9obiBMaW4gKKpMtMK31yk=?= wrote:
>Dear SI gurus,
>
>One question regarding SI simulation for SCSI backplane. How do I define
>the worst case of SCSI backplane with 15 slots for 15 SCSI drives?
>
>Shall I do the SI simulation, theoretically, for all combinations of 15
>SCSI drives?
>There are huge combinations -- the number of drives mixed with the number
>of slots (location on the backplane). Based on my knowledge, I would like
>to put drives on even spaces for the best case of SI simulation. for
>example, three drives on slot 1st,8th, and 15th. For the worst case,
>intuitively, I would like to put them on slot 1st,2nd, and 3rd because of
>far away from end terminators.
>
>The question is that how to assure the worst case for simulation? Or,
>doing all combinations is only way to do even it is exhaustive.
>
>Your comments are highly appreciated.
>
>Best Regards,
>
>John Lin
>Senior SI Engineer, Server Team, ARD4
>Quanta Computer Inc.,Taiwan, R.O.C.
>Email: John@quantatw.com>Tel: 886+3+3979000 ext. 5183
>

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